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Il6 NEW YORK STATE MUSEUM 



This occurrence of volcanic rock merits detailed description, both 

 because it is unique and because it is puzzling. It is unlike any 

 other known occurrence of igneous rock in the State or in the 

 neighboring states. 



Woodworth's original description of the knob is so excellent 

 that we can not do better than to quote freely from it : 



The right bank of the Hudson river here consists of the usual bluff of 

 Hudson River slates partly masked by Pleistocene clays. The igneous rock, 

 being more resistant to erosion than the fragile slates, has withstood better 

 the glacial erosion to which the region has been subjected and therefore stands 

 out as a sort of buttress from the main wall of the inner Hudson valley or 

 gorge. Much Hke the volcanic necks and plugs about Edinburgh in Scotland, 

 this hard mass has been deeply scoured at base on the ice-struck side. In 

 fact, all of the present relief of this plug and the adjacent river valley is due 

 to the action of the river combined with that of the ice sheet of the glacial 

 period. 



The summit of the knob scarcely attains the level of the upland which lies 

 west of the river. A slight depression west of the plug serves to give it the 

 appearance of a low knob when viewed from the upland, but at a distance 

 it is relatively inconspicuous. This fact, taken in connection with the dark 

 color of the rock in which respect it closely resembles the adjacent Hudson 

 series, perhaps accounts for its going so long unnoticed or at least un- 

 described by the geologists who have passed through the upper Hudson 

 valley. There is no mention of the knob by Peter Kalm or later observers ; 

 yet it appears from Brandon's historical map of Old Saratoga that General 

 Stark of the American army occupied the eastern base of this knob during 

 the Battle of Saratoga. 



Stark's knob igneous mass lies surrounded on the ground by the Hudson 

 River (Normanskill) slates. These are highly inclined, cleaved, and much 

 broken rocks with a general northeast strike. So far as my own observations 

 go, there are no small dikes radiating from the main igneous mass into 

 the adjacent cleaved sedimentary rocks, nor are there any noticeable signs 

 of metamorphism in these rocks attributable to the heating action of the 

 lavas in the plug. The Hudson river group throughout this region is some- 

 what altered, but not more so at Stark's knob than remote from it. . . . ■ 

 This lack of contact metamorphism, unless such alteration be limited to 

 baking, which was not observed in the accessible portion of the contact, and 

 the failure of apophyses or branching dikes, are points of little value in 

 determining the origin of the igneous rock in the knob. It remains to 

 determine by other evidences whether the rock is intrusive or extrusive. — 



On the southeast side of the igneous mass and dissecting its border are two^ 

 faults ; that on the eastern side strikes n. 9° e., that on the southeast, n. 54° e. 

 The southeastern fault is downthrown on the northwest, as on this side there 

 is to be seen the slate underlying a mass of trap on the southeast of the 

 fault. The complete relations of the igneous to the sedimentary rocks on 

 this side are not shown. Figure 9, which is a diagrammatic representation 

 of the cross section of the knob and its peculiar internal structure, shows 



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